Fat Guy MiniBike

C

Canadian Kid

New Member
#1
#1
Ok, guys I need some advice. So I bought an old Manco trike, pictured below. And I want to convert it to a fat guy minibike….

So the trike has an 8hp Briggs and a 40 series clutch on it. My idea is to narrow and lengthen the rear end so I can fit the rear tire without repositioning the shaft bearing mounts. Basically do some cutting and splicing. And leave everything else well enough alone.

My biggest questions are with the motor and 40 series clutch, what gear ratio should I be looking at? The kicker, I’m 6 foot 4 inches tall and am pushing 350 lbs. Tires will be 22x11x8, and really if I hit 25 mph I would be plenty happy. I would much rather have low end than top speed. From what I’ve read more weight equals larger ratio. I should be able to source sprockets that get me 12:1 ratio but is that needed with the 40 series clutch? By the calculators I found online 12:1 will only get me about 20mph where 9:1 will get me approx. 26 mph. Is the 8hp even big enough?

Let me know what you guts think, any insight you can give me is greatly appreciated.

Canadian Kid

$_20.jpg IMG_0827.JPG
 
capguncowboy

capguncowboy

Well-Known Member
#2
#2
I actually have a Manco Rustler that was converted into a 2-wheeler. It was done long before I aquired it, but it's extremely fun to ride. I'd be happy to take some measurements, though. Just PM me. I can tell you that the braces for the footpegs were removed from the bike, and the foot pegs were welded directly to the engine plate. This gives you a little more room to lean into a turn. I'm not sure what all of the rear end is original, and what was added/removed. The front forks were also extended (you can see the welds), to give it a little more of a full-size bike look.

I put a 7HP Kohler engine on mine, and it uses a jackshaft to gear it from 1/2 (12T clutch, 24T input, 12T output, to a 72T rear sprocket). It pulls me (210 lbs) just fine up hills, but it can't climb a steep hill if I don't have at least some momentum first.

When I first got it



Mocked up the engine



After taking it for a ride




I have an ATV seat for it, but haven't taken the time to modify and install it yet.
 
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capguncowboy

capguncowboy

Well-Known Member
#3
#3
BTW, I'm 6'5", so I'm in your neighborhood. Mine wasn't extended, and it's plenty big enough for me (especially compared to a few 60s mini bikes I've ridden). I'd keep the TAV if you can. It's going to be much better than a Centrifugal clutch, especially when you're taking off or going up hills.

I'm excited to watch your build. I've been planning on doing a bottom up cleaning/restoration on mine (keeping it a 2-wheeler) for a while, but haven't had the time
 
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C

Canadian Kid

New Member
#4
#4
I'm only lengthening the back end simply to make enough room to get the the back tire between the hitch mount and driven part of the clutch once its installed close to its original location.

capguncowboy, for some reason i cant see your pics.
 
capguncowboy

capguncowboy

Well-Known Member
#5
#5
Canadian Kid said:
capguncowboy, for some reason i cant see your pics.
Click to expand...
They're hosted through dropbox.com. Sometimes that site is blocked at workplaces and the like. Are you on your home PC or at work?

The rear of my bike wasn't lengthened at all and the wheel fit just fine. At least, I don't think it was lengthened comparing it to your pics of a stock frame
 
C

Canadian Kid

New Member
#6
#6
Sure looks like welds on the bar between the hitch and the flange bearing. Looks like there has been about 6 inches added in there. And that's exactly what I figure I need to do.
 
bigrob

bigrob

#12
#12
I have a manco bigcat , probly the closest stock bike to what you are
planning on building with 22-11-8 tires

I have a princess auto 6.5hp clone on it with a comet 30 series ? torque converter
The output sprocket is a 14 tooth to a monster rear sprocket that has 80 teeth

I weigh aprox 285 and it hauls me no prob , will wheelie from a dead stop and climb anything
 
H

Havasu Dave

Moderator
#13
#13
You're asking for ratios with a viable drive system. They're near infinite. Even the Comet 20 system is large enough for your engine and weight.

A TAV system is available in that size, but you don't say if you're going to convert to a swing arm, or simply weld to the back of the frame.

If I had this project in mind, I'd certainly consider a swing arm/suspension bike. In that case, I wouldn't use a TAV system, but a driver/driven, and hopefully by refurbishing the existing 40 series drive. Then a jack shaft near the swing arm pivot.

That is more complicated, but not overly so. Then again, a cushy seat and fat tires might make suspension a waste.
 
C

Canadian Kid

New Member
#14
#14
Havasu Dave said:
If I had this project in mind, I'd certainly consider a swing arm/suspension bike. In that case, I wouldn't use a TAV system, but a driver/driven, and hopefully by refurbishing the existing 40 series drive.
Click to expand...
I think I need a little educating. what is the difference between a TAV and a driver/driven? isnt a TAV simply a driver/driven on a mounting plate?

i want to reuse what was there as much as possible. I guess i could just buy new sprockets to replace what is already there, but i wasnt sure if a higher ratio would be better based on my size/weight.

Canadian Kid
 
capguncowboy

capguncowboy

Well-Known Member
#15
#15
Havasu Dave said:
Then again, a cushy seat and fat tires might make suspension a waste.
Click to expand...
I keep my tires inflated at a really low pressure (22x11-8 on the front and 21x12-8 on the rear) and they absorb most of the bumps and it does great. However, if you drive over a curb or a hump, it can get sketchy. Suspension would really help, but if you're careful, it's not necessary.
 
capguncowboy

capguncowboy

Well-Known Member
#16
#16
Canadian Kid said:
I think I need a little educating. what is the difference between a TAV and a driver/driven? isnt a TAV simply a driver/driven on a mounting plate?

i want to reuse what was there as much as possible. I guess i could just buy new sprockets to replace what is already there, but i wasnt sure if a higher ratio would be better based on my size/weight.

Canadian Kid
Click to expand...
TAV is a Torque-A-Verter. It's just Comet's name for their Torque Converter, which you already have. I would definitely rebuild that one rather than buy an all-new one. As Dave said, the ratios on a TC is nearly infinite. As you rev up the engine, the pully changes size on the front. Once you start moving, the rear one changes size too, constantly changing the gear ratio. For your size, it's the best avenue.
 
C

Canadian Kid

New Member
#19
#19
capguncowboy said:
TAV is a Torque-A-Verter. It's just Comet's name for their Torque Converter, which you already have. I would definitely rebuild that one rather than buy an all-new one. As Dave said, the ratios on a TC is nearly infinite. As you rev up the engine, the pully changes size on the front. Once you start moving, the rear one changes size too, constantly changing the gear ratio. For your size, it's the best avenue.
Click to expand...
i definetly will be sticking with what is already there, i just wasnt sure what would be a good gearing ratio to run off the converter... considering my size i was unsure if a higher ratio was warranted with the Converter.
 
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